Electronics > Projects, Designs, and Technical Stuff
'Ripple' Current vs 'Ripple' voltage
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jaunty:
okay -so here's a bit of a technical question ... or maybe an abstract one ...

I KNOW the term 'ripple current' is generally associated with capacitor spec'ing etc ...but earlier i got into a bit of an argument with someone over use of the term 'ripple current' in relation to talking about how well regulators work in a power supply and how i must be some kind of idiot or jerk for using the term ... they seemed quite offended at any rate. SO - i thought i'd ask. I mean - voltage and current really aren't THAT separable are they - they are both simply a different manifestation or measurement of the same electron flow - no? if you've got a measured ripple in voltage then wouldn't you also have a 'ripple' in measured current too? where should the terms be used or not used then?
james_s:
Ripple current is what you get when you push a rippling voltage into a load. It's no different than the way current is what happens when you have voltage feeding a load.
Siwastaja:
The terms are pretty self-explanatory if you understand the concepts of current and voltage, aren't they?

Ripple current is the AC part of the current in a supposedly DC current system. Ripple voltage is the AC part of the voltage in a supposedly DC voltage system.

For a voltage source, the voltage ripple spec is important, since that's what's claimed to be regulated. Current ripple would vary massively depending on the load.

For a current source, the current ripple spec is important, for the same reason.

Note that internally, they lead to each other. For example, many switch mode topologies are designed around having a massive (around 30% of the maximum output current) ripple current in the inductor. The output capacitor equivalent series resistance (> 0) converts that current ripple to unwanted voltage ripple by standard Ohm's law.

(AC) ripple current is a relevant spec for a capacitor, since only AC current flows in capacitor, causing resistive heating (I^2 * R), shortening the lifetime. You can, of course, give a AC voltage rating for the capacitor as well, since a specific AC voltage waveform would generate a specific AC current waveform, causing the same heating. This is a simple conversion calculation. Depends on the intended application which one (or both) are given in the datasheet.

Maybe you used a funny wording in your argument? Some people are extremely pedantic and expect the "standard" way of expression, like they learned it from a book. I don't think this is the best way, even when they are right, and even if I were wrong. A fresh look from a different angle, using nontypical terminology to express the same, helps learning and understanding, and is more important than who's technically right.
jaunty:
thanks for the 'splaining ... yes i'm sort of constantly using different terms for things and 'trying out' lexical variations so i suppose i shouldn't be at all surprised when it happens ... electronics is very tricky for creativity however - i mean it's complicated enough just looking at things in a sort of 'status quo' way and figuring out what was going on ... i'm always driving myself nuts thinking of stuff like 'what if signal were to flow THIS WAY - backwards through and inductor say or be induced on this track - what then? gahhh

actually -total logical jump here ... i was thinking of starting a topic here about pitfalls to learning - misunderstandings that we may have been under for a long time that hampered learning ... i certainly have more than my fair share! the forum has been great for helping with that stuff though
Conrad Hoffman:
Ripple current through a capacitor is what heats it up and shortens the life. It's very hard to calculate and is best measured. Ripple voltage from a regulator or power supply may feed through downstream circuits, causing hum in audio systems or other problems. It's usually measured as a voltage. Obviously voltage and current go hand in hand, but often one is more illuminating than the other in understanding a circuit.
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